Problem: $ { {-3} \times \left[\begin{array}{rr}{2} & {4} \\ {-1} & {0}\end{array}\right] = {?} } $
Solution: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rr}{-3}\times{2} & {-3}\times{4} \\ {-3}\times{-1} & {-3}\times{0}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{-6} & {-12} \\ {3} & {0}\end{array}\right]}$